滇西北石鼓岩群新元古代变质基性岩锆石U-Pb定年及地质意义

滇西北石鼓岩群位于羌塘-三江造山系中咱-中甸地块南缘丽江地区石鼓-巨甸一带,石鼓岩群变质岩系中发育的新元古代变质基性岩是Rodinia超大陆裂解的重要构造-岩浆记录。通过对石鼓岩群中的变质基性岩岩石学、地球化学的研究表明,其主要为大洋拉斑玄武岩,具有介于EMORB与OIB之间的地球化学特征,岩浆起源于富集地幔区,是尖晶石地幔橄榄岩部分熔融的产物,并经历了地壳的混染作用。LA-ICP-MS锆石U-Pb定年表明石鼓岩群变质基性岩形成于新元古代中期(833.9±3.5Ma),时代与扬子陆块西缘大量分布的新元古代岩浆岩一致,其形成可能与该时期的地幔柱活动有关。

Zircon U-Pb dating and geological significance for Neoproterozoic metabasite of the Shigu group in northwestern Yunnan

The Shigu group in southern margin of the Zhongzan-Zhongdian block of Qiangtang-Sanjiang orogenic system is located in the Shigu-Judian area of Lijiang.The Neoproterozoic metabasite in metamorphic series of the Shigu group is an important tectonic-magmatic record of the Rodinia supercontinent breakup.Based on petrology and geochemistry research,it is indicated that the metabasite in the Shigu group is mainly oceanic tholeiite with the characteristics between E-MORB and OIB.The magma was originated from enriched mantle,which is product of spinel mantle peridotite partial melting,with crustal contamination.LA-ICP-MS zircon U-Pb dating indicates that the metabasite in Shigu group was formed during Mid-Neoproterozoic (833.9 ± 3.5 Ma),consistent with the many Neoproterozoic magmatic rocks from the western margin of Yangtze block,which was probably related to mantle plume activity of that time.